The Suprachiasmatic Nucleus is a small, bilateral cluster of neurons located in the anterior hypothalamus, recognized as the body’s central pacemaker, or master clock. This nucleus is responsible for generating and regulating circadian rhythms, which are the approximately 24-hour cycles that govern sleep-wake patterns, body temperature, and hormonal secretion. Its integrity is vital for maintaining temporal organization of physiological functions.
Origin
The SCN was identified as the anatomical location of the master circadian clock in the early 1970s through lesion and transplant studies in rodents. The term combines supra (above) and chiasmatic (referring to the optic chiasm), indicating its precise anatomical location just above the optic nerve crossing. Its function connects light input directly to endocrine and behavioral outputs.
Mechanism
The SCN generates its rhythmic output through an intricate, self-sustaining molecular clock composed of interlocking transcriptional-translational feedback loops involving ‘clock genes’ like Per and Cry. Light input, transmitted directly from the retina via the retinohypothalamic tract, entrains this clock to the 24-hour solar day. The SCN then projects signals to other brain regions and endocrine glands, notably the pineal gland to regulate melatonin release, thereby synchronizing peripheral clocks and orchestrating systemic circadian hormonal rhythms.
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